Solid film prelubricants are used in several metalworking operations including stamping, drawing, forging, blanking, bending, rolling, cutting, grinding, punching, sawing, hobbing, reaming, spinning, extruding, trepanning, coining, swagging and the like. Solid film prelube emulsion lubricants improve the production of formed parts for the automotive, appliance, food container and general manufacturing industries. In these industries, sheet metal is formed into specific shapes by the use of mechanical presses. Such general metal-working operations can be further categorized into stamping and drawing.
Stamping includes all forming operations where parts are formed from sheet metal without a change in the gauge or thickness of the sheet metal. Drawing defines all forming operations where there is a change or reduction in the gauge or thickness of the sheet metal. Shallow drawing is the forming of a cup or shape no deeper than one-half its diameter with only small reductions in metal gauge or thickness. The forming of a cup or shape deeper than half its diameter with substantial reductions in metal thickness or gauge is known as deep drawing. Formed parts for the automotive, appliance, food container and general manufacturing industries may be produced by one or a combination of these stamping and drawing operations.
Heat generated during the course of such operations can adversely affect the outcome of the operations, changing the metallurgical properties of the sheet metal and tooling, resulting in undesirable effects such as staining and oxidation of the metal. During typical metal-forming operations, temperatures attained can be as high as 180-190.degree. F. which temperatures are higher than the melt points of prior art solid film prelubricants, such as those described in U.S. Pat. Nos. 5,091,100 and 4,846,986, as well as co-pending application Ser. No. 07/906,167, the teachings of which are herein explicitly incorporated by reference. Reducing the coefficient of friction for a specific forming process serves to minimize heat generated during the forming operations, reduce power requirements, reduce tool wear and eliminate blocking or adhesion between the sheet metal and tooling during the forming operations, transit and storage of the formed parts. Forming lubricants, especially solid film prelube emulsions, reduce the friction that occurs between the metal being formed and the tooling employed for the forming operation, and between metal pieces during storage, handling and forming. However, the beneficial effects of the use of prelubricants are significantly diminished in applications where the operating temperature of the forming apparatus-exceeds the melt point of the solid film prelube, resulting in degradation of the lubricating effect of the composition. Consequently, there exists a need for a solid film prelubricant that possesses a sufficiently high melt point, preferably in excess of 200.degree. F., that will enable the composition to be used in forming operations generating high temperatures. More importantly, it is desirous that such a prelubricant composition, forming a high melt point solid film prelube layer on treated metal, retain the desirable performance characteristics, such as lubrication, cleanability, metal compatibility, etc., needed for successful application.
Prior to the development and use of prelubes, a single composition could not provide both adequate lubrication for a metalworking forming process as well as corrosion protection for the metals involved. According to prior art practices, metal coils would arrive at a processing site, such as a stamping plant, coated with a rust preventative oil to protect against corrosion. Between the steps of blanking and the actual forming operation, the rust preventative oil was removed by a cleaning operation using an alkaline cleaner, solvent cleaner or blank wash oil. A hydrocarbon oil-based forming lubricant would then be applied to the sheet metal before the stamping or drawing operation. In addition to requiring separate corrosion resistance and lubrication treatments, the removal of the corrosion inhibitor would also create a significant volume of waste fluids generated during the cleaning process. These waste fluids would then present additional problems of handling, storage and disposal due to their potentially hazardous character.
In the last decade, this tedious process of using separate rust preventative oils and drawing lubricants has been replaced by the use of a single prelube composition. Prelubes thus function as both a corrosion preventative and a forming lubricant. Either hydrocarbon oil-based or solid film prelubes are applied at the sheet metal mill during either temper rolling or inspection. Thus, no modifications to physical equipment or processes are needed within the sheet metal mill to use prelubes, as the application of prelubes merely replaces the application of rust preventative oils. Advantages are obvious, in that prelube compositions do not need to be removed from the sheet metal until after the blanking and forming operations. Thus, the use of such prelube compositions eliminates the cumbersome, multi-step process of applying and removing the combination of rust preventative oils and forming lubricants before forming operations. There exists a continuing need for compositions which both adequately prevent corrosion and provide lubrication to ferrous and nonferrous metals during forming operations.
The advantages obtained by the efficiency of using a prelube, however, would be diminished or nullified if unusual methods were necessary to remove the lubricant from the final product. Some substances with lubricating properties, for instance wax films, cannot be easily removed with alkaline cleaners and thus their use entails a serious detrimental effect on the efficiency of overall operations.
In addition to lubrication and corrosion protection, a prelube composition must be removable, nonstaining to the metal and compatible with other chemicals used in producing formed metal parts. In order to prevent interference with all future processing operations after forming, all traces of the prelube composition must be removed from the metal surface of the formed part. In most industries relying on formed metal parts, powdered or aqueous alkaline and acid cleaners are typically utilized for removing lubricant compositions. Such cleaner compositions are water soluble at the recommended dilutions and are strongly alkaline or acidic in nature in order to effectively remove all traces of processing lubricants from a wide variety of metal substrates. Many prelube compositions, especially hydrocarbon oil-based systems, contain chemical additives that cannot be easily removed with such cleaners, thereby having a detrimental effect on all future processing operations and even limiting potential applications for the formed metal parts. A need exists for compositions with improved cleanability from metal substrates as compared to the other prelubes used on such substrates, including hydrocarbon oil-based and dry film lubricant compositions.
Metal coils coated with prelube compositions can be stored for indefinite periods of time before being stamped or drawn into parts. Many chemical constituents of such prelube compositions can oxidize to varying degrees during storage. Oxidation byproducts from hydrocarbon oil components can adversely affect metal surfaces causing staining, discoloration, etching or pitting of the outer atomic layers of the metal strip. Automotive, appliance, food container and general manufacturing industries require prelube compositions that will protect metal substrates against conditions of oxidation and will not cause contact staining during storage.
Prelubes must also be compatible with other processing chemicals and operations following forming operations. Many formed parts often have severe bends or angles formed during fabrication operations. These bends and angles can create flanges, seams or other tight radii where prelube compositions can become entrapped. Even with normal exposure to alkaline cleaners, trace amounts of prelube can remain out of reach within these intricate areas. Although prelube compositions may be effectively removed from exposed part surfaces, trace amounts of prelube remaining on the formed parts can be volatilized or otherwise released during subsequent processing operations potentially contaminating those processes. This situation necessitates that such prelube compositions, especially solid film prelube compositions, be compatible with cathodic electrocoat paint primers, adhesives used to bond structural components together, as well as any type of welding or post welding operations. In additions, for applications where the formed metal is used in the manufacture of beverage or other food containers, whatever trace amounts of lubricant remain after cleaning must be compatible with the food or beverage to be stored in the containers.
The prelubes commonly used in manufacturing industries such as the automotive industry are hydrocarbon-based compositions containing sulfurized or waxy components, liquid at ambient room temperature. These compositions tend to drain off the metal surfaces, creating maintenance problems, and further tend to be or become unevenly distributed on the metal surfaces due to capillary forces. The properties of rust prevention and drawing assistance both depend in significant part on uniformity of the lubricant film. Such tendency to puddle on the metal surface diminishes a lubricant's potential in providing protection from rust and in facilitating the stamping or drawing operations. Thus, these industries desire a prelube that provides lubricant film uniformity and film strength undiminished during shipping and storage periods, Further, film strength is a particularly significant property for facilitating drawing operations; a lubricant having high film strength will permit more severe draws to be made. The prelube compositions of the present invention provide a uniform, homogenous and consistent film morphology and structure on a metal substrate.
Often, prior art prelube compositions must be applied at coverage rates up to 1000-2000 mg/ft.sup.2 in some applications to provide the required performance. Many industries desire prelube compositions that can offer effective performance at lower coating weights thereby improving overall cost efficiency of the forming operation. An advantage of the compositions of the present invention is effective performance on metal substrates at lower coating weights (between 20 and 500 mg/ft.sup.2), which substantially improves forming lubricant cost performance.
All prelube compositions must lend themselves to improving housekeeping and cleanliness conditions at the mill and at the manufacturing plant. Often, hydrocarbon oil-based lubricants and some solid film prelubes can leak onto machine and work surfaces or volatilize into the atmosphere creating a hazardous work environment. Prelubes can often create irritation or dermatitis among employees exposed to the compositions. The compositions can also contaminate floor trenches around forming presses, thereby often reaching waste treatment streams. The prelube compositions of the present invention are non-hazardous and do not contaminate the work environment.
A prelube composition must be compatible with waste treatment processes and chemicals. Prelube compositions entering waste streams must have minimal to no effect on the streams and be classified as waste treatable. The prelube compositions of the present invention are compatible with existing waste treatment schemes because they are treatable by conventional waste treating processes and enter the waste treating processes at significantly lower levels.